The present invention relates generally to interlocking closure devices for thermoplastic storage bags, and more particularly, to an interlocking closure device which produces an audible sound when the closure device is being open or closed. Further, the closure device provides a vibration or bumpy feel, which is tactile and readily perceptible to the touch when the closure device is closed.
The use of closure devices for fastening storage containers, including plastic bags, is generally known. Furthermore, the manufacture of closure devices made of plastic materials is generally known to those skilled the in the art, as demonstrated by the numerous patents in this area.
A particularly well-known use for closure devices is in connection with flexible storage containers, such as plastic bags. In some instances, the closure device and the associated container are formed from thermoplastic materials, and the closure device and the sidewalls of the container are integrally formed by extrusion as a single piece. Alternatively, the closure device and sidewall of the container may be formed as separate pieces and then connected by heat sealing or any other suitable connecting process. In either event, such closure devices are particularly useful in providing closure means for retaining matter within the bag.
Conventional closure devices typically utilize a thermoplastic zipper in the form of mating fastening strips or closure elements, which are used to selectively seal the bag. The fastening strips comprise interlockable male and female profiles. With such closure devices, however, it is often difficult to determine whether the fastening strips are fully occluded. The problem addressed by the present invention pertains to the determination of closure or nonclosure of the zipper of a reclosable thermoplastic bag.
One technique for aiding in the determination of the state of zipper is to utilize a zipper that imparts a visual color change upon closure. Different colors may be utilized in each of the opposing zipper profiles to produce a third distinct color when interlocked. Zippers utilizing such a color change are seen in U.S. Pat. Nos. 4,186,786 and 4,285,105.
It is well understood that all thermoplastic zippers have an occlusion and peel force. It is also known that a desired audible and/or tactile effect can be achieved during opening or closure of the zipper by changing the occlusion and peel force along the length of the zipper. One technique for changing this force is to remove portions of one or both of the male and female zipper profiles such that there is a discontinuity in structure in those portions of the opposing profiles which contact each other upon interlockment of the zipper. Examples of zippers having closure profiles with portions removed are disclosed in U.S. Pat. No. 5,070,584 to Dais et al. and U.S. Pat. No. 5,647,100 to Porchia et al.
In U.S. Pat. No. 5,070,584, at least one of the zipper profiles includes indentions within and intermittently along its length along a surface of it adjacent a portion of the opposing profile. The indentions are present in and along a part of the zipper profile interlockable with a part of the opposing zipper profile wherein both of the interlockable parts are longitudinally extending. The indentions and the surfaces which define or bound the indentions of the part of the zipper profile are adjacent the part of the opposing zipper profile with which it is interlocked. This patent further discloses that the part of the zipper profile having indentions therein is substantially free of interdigitation with the part of the opposing zipper profile with which it is interlockable. According to this patent document, being xe2x80x9csubstantially free of interdigitationxe2x80x9d means that the cavities defined by the indentions within the part are substantially free of intrusion by portions of the part of the opposing profile. The indentions in the bulbous head of the male closure profile provide the structural discontinuity in the region of interlocking contact with the female closure profile that creates the desired audible clicking sound and/or tactile effect.
In accordance with the preferred method of making the above-described audible/tactile zippers, a rotary punch apparatus is used to laterally punch out segments of the bulbous head of the male closure profile to form indentations along its length. The punching is lateral as it occurs in a direction that is perpendicular to the extension of the bulbous head. In the final assembly of the zipper bag, the interlocking male and female profiles are then brought together in a separate step before being attached to the opposing bag side panels. A method of making an audible/tactile zipper closure wherein the interlocking closure profiles are made structurally discontinuous while interlocked to each other would be desirable as it would reduce the number of steps in the final assembly of the zipper bag.
The punching technique described above also generally requires careful attention to profile positioning and alignment of the zipper profile through the deforming apparatus to ensure against removal of too much profile material, which otherwise results in the increased likelihood or incidence of liquid leakage through the interlocked zipper. The zipper profiles disclosed in the ""584 patent have enjoyed much commercial success. However, there still exists a need for alternative and improved thermoplastic closure members that impart a vibration perceptible to the touch, and emanate an audible clicking sound along the closure member""s length when being closed or interlocked so that the fact of closure can be confirmed by a nonvisual means, i.e., by sound and feel.
Accordingly, it is desired to provide a reclosable bag having an improved closure member that imparts a vibration perceptible to the touch, and, further preferably, emanates an audible clicking sound continually along the closure member from end to end; and it is desired to provide a method for production of the reclosable bag wherein material is not removed from the closure region such that leak resistance through the closure is improved.
The present invention provides a closure device for a thermoplastic bag which includes two opposing, longitudinally extending interlockable male and female fastening strips having respective male and female closure elements or profiles that are deformed to interdigitate and produce an audible clicking sound and or tactile effect that is perceptible to the touch as the closure device is opened and closed. Interdigitation of the two profiles is achieved by cold forming the profiles while interlocked. The shape of the cold form is a stepped deflection of both profiles so that their shapes are generally congruent. The stepped deflections provide a change in the occlusion and peel force of the interlocking closure device thereby resulting in an audible clicking or popping sound as the closure device is opened and closed and a tactile effect that is perceptible to the touch as the closure device is closed.
In accordance with an advantageous aspect of the invention, the compressive force across the stepped deflection is graduated such that the greatest amount of compression is experienced at the outermost or uppermost portion of the closure profiles. In this way, leak resistance through the closure device is improved and the desired audible and/or tactile effects are still achieved.
Methods and apparatus which incorporate the features described above and which are effective to function as described above constitute further, specific objects of the invention. Other objects and advantages of the invention will become apparent upon reading the following description and upon reference to the drawings.